thunder15j
Member
- Location
- Cali
A customer is asking me to design and provide cost estimates for a direct burial 480 volt single phase feed to a transformer at the other end that will provide 120/240 single phase power to a building. The run is to be several thousand feet on this rural ranch setting. We are estimating the secondary load to be around 50 amps @ 120/240V. Voltage drop calulations are pretty cut and dried using one of several wire mfgs Vd charts. I realize that large conductors would be needed. A typical installation would be to run 2 480V current carrying conductors (l1,L2) and an equipment carrying conductor. At the transformer at the out building, a ground rod or similar electrode would be installed and that would be bonded to the nuetral of the secondary of the newly created 120/240V system.
However, is there a safe way of eliminating the EGC that would normally be run with the 480 volt feed (for cost issues)? Maybe an isolation transformer on the feed side. I know that under normal circumstances that simply driving a ground rod at the far end and bonding to secondary neutral will do little to clear a 480 volt fault if no grounded conductor is installed. The earth is not that great a conductor. Kind of like driving a ground rod attempting ground metal light poles to clear a fault-virtually useless (except for lightning).
I am not advocating eliminating the EGC. I normally run EGC with everthing, especially in the smaller sizes. Just wondering if a SAFE alternative would work. I pretty much already know the probable answer. We also might consider medium voltage (4160).
However, is there a safe way of eliminating the EGC that would normally be run with the 480 volt feed (for cost issues)? Maybe an isolation transformer on the feed side. I know that under normal circumstances that simply driving a ground rod at the far end and bonding to secondary neutral will do little to clear a 480 volt fault if no grounded conductor is installed. The earth is not that great a conductor. Kind of like driving a ground rod attempting ground metal light poles to clear a fault-virtually useless (except for lightning).
I am not advocating eliminating the EGC. I normally run EGC with everthing, especially in the smaller sizes. Just wondering if a SAFE alternative would work. I pretty much already know the probable answer. We also might consider medium voltage (4160).